Analogy could help engineers develop materials that make use of repeating patterns…

Using a new mathematical methodology, researchers at MIT have created a scientifically rigorous analogy that shows the similarities between the physical structure of spider silk and the sonic structure of a melody, proving that the structure of each relates to its function in an equivalent way.

The step-by-step comparison begins with the primary building blocks of each item — an amino acid and a sound wave — and moves up to the level of a beta sheet nanocomposite (the secondary structure of a protein consisting of repeated hierarchical patterns) and a musical riff (a repeated pattern of notes or chords). The study explains that structural patterns are directly related to the functional properties of lightweight strength in the spider silk and, in the riff, sonic tension that creates an emotional response in the listener. Continue reading »

Research conducted at the University of Michigan College of Engineering may lead to the use of insects to monitor hazardous situations before sending in humans.

Professor Khalil Najafi, the chair of electrical and computer engineering, and doctoral student Erkan Aktakka are finding ways to harvest energy from insects, and take the utility of the miniature cyborgs to the next level.

“Through energy scavenging, we could potentially power cameras, microphones and other sensors and communications equipment that an insect could carry aboard a tiny backpack,” Najafi said. “We could then send these ‘bugged’ bugs into dangerous or enclosed environments where we would not want humans to go.”

According to the American Museum of Natural History, a total of 42,473 spider species, belonging to 110 different families, have so far been described worldwide. Within this spinning, many-eyed, predatory multitude, an astonishing 4,401 species—or over a tenth of the total diversity of the order—are accounted for by the members of a single family, the Linyphiidae.

Also known as sheet-weavers, because their webs consist of horizontal skeins of silk that seem to hang in the air like taut white bed linens being grasped by invisible hands, these marvelous creatures are a cosmopolitan lot. They have been observed occupying all manner of different habitats, virtually all over the world: on seashores, in deserts, hidden among the vegetation of forest floors, and even burrowed under the blankets of mountain snowfields. (Darwin himself wrote that he had seen “vast numbers” of them lashed to the rigging of the Beagle). And they’re often encountered in almost fantastic profusion: nearly two million individuals, laments one guide to agricultural contaminants, can occur within a single acre of farmland.

As with other social insects, it was once thought that workers were essentially equivalent in ant colony hierarchies. But it appears that a few well-informed individuals shape group decisions by leading nestmates to new homes.

The findings could add a new dimension to ant-derived models of self-organization.

“Although self-organized systems appear very effective under the assumption that all individuals follow the same simple set of rules, the presence of key, well-informed individuals altering their behavior according to their prior experience might generally enhance performance even further,” wrote biologists from the University of Bristol and the University of Toulouse in an Aug. 24 Journal of Experimental Biology paper.

To study nest-hunting, Nathalie Stroeymeyt and colleagues Nigel Franks and Martin Giurfa collected “house-hunting” ants, or Temnothorax albipennis, from the southern coast of the United Kingdom. These small, light-brown ants make simple sand-enclosed nests in the cracks of rocks.

Moving the ants into the lab, Stroeymeyt gave them a well-supplied artificial nest. She then placed an identical empty nest site at the opposite end of the ants’ territory. Each ant’s back was painted with individually-identifiable colored spots. Webcams and motion-detection software allowed the researchers to keep track of the movements of specific ants.

One week later Stroeymeyt placed a second unfamiliar nest site in the territory and destroyed their original home. Though some ants began to run around randomly in all directions, a few ants who had already explored the alternate nest site headed directly to it.

Those ants then quickly returned to the destroyed nest to recruit followers. They repeated the process until enough had gathered at the new nest site to relocate the entire colony.

Most studies of how ants find new nest sites use colonies unfamiliar with a new territory, and assume that all workers follow the same rules. But that’s not realistic, and as a model for self-organization and distributed decision-making — ants have inspired various forms of traffic coordination, from cars to data — it might not be optimally efficient.

“This begins to change how we think about self-organization,” said Nicola Plowes, a behavioral ecologist and ant specialist at Arizona State University, who was not involved in the research. “Informed individuals making those decisions actually result in a process that is more efficient than a simple homogeneous self-organized system.”

The findings will be exciting for technologists and mathematicians who use insect-based algorithms, Plowes believes.

“Sky Harbor International Airport, for example, uses ant-based algorithms for its baggage carriers,” she said. “Knowing that we can incorporate informed individuals, you can actually make it work better and faster.”

UA researchers have uncovered evidence in ant colonies suggesting that social networks may function differently than previously assumed.

Be it through the Internet, Facebook, the local grapevine or the spread of disease, interaction networks influence nearly every part of our lives.

Singled out by unique color codes, ants provide evidence through their interactions that challenges previous assumptions about how social networks function. (Photo courtesy of Benjamin Blonder)

Scientists previously assumed that interaction networks without central control, known as self-directed networks, have universal properties that make them efficient at spreading information. Just think of the local grapevine: Let something slip, and it seems like no time at all before nearly everyone knows.

“Many people who have studied interaction networks in the past have found them to be very efficient at transferring resources,” said Blonder. “The dominant paradigm has been that most self-organized networks tend to have this universal structure and that one should look for this structure and make predictions based on this structure. Our study challenges that and demonstrates that there are some interaction networks that don’t have these properties yet are still clearly functional.”

“There are a huge number of systems that are comprised of interacting parts, and we really don’t have a good sense of how these systems are organized,” said Blonder. “Think of a city with many people or the Internet with many computers. You have all these parts doing their own thing and somehow achieving some greater function.”

The researchers chose to use ant colonies as models for self-directed networks because they are comprised of many individual components – the ants – with no apparent central organization and yet are able to function as a colony.

“We think no individual ant has a sense of purpose,” said Blonder. “It doesn’t go out one day and say: ‘I’m going to move this pebble for the greater good of the society.’ It has a behavioral program where if it sees a pebble, then it’s likely to move it. The reason that contributes to the good of the colony is an evolutionary argument where the ants’ behavior is shaped over thousands or millions of generations.”

Dornhaus and Blonder studied colonies of Temnothorax rugatulus, an ant species that is common in southern Arizona.

“These ants like to live in little rock crevices such as underneath a rock or in a split in the rock,” said Blonder. “The trick is convincing them to go from their nice little home on Mount Lemmon to the lab.”

Which raises an interesting question: How does one collect an ant colony?

“It isn’t easy,” said Blonder. “You get an aspirator, which is a tube with a fine mesh on the end of it so you don’t inhale the ants, and you put the tube down in the colony and you suck. And the ants come up and you blow them out into a container to transport them to the lab.”

“Of course, once you flip the rock over, the ants are upset. You have to get them before they all run off somewhere. And you also have to get the queen because without the queen the colony will die.”

The queen, the mother ultimatum among ants, is the only member of the colony that reproduces. Without her, there would be no new ant workers and the colony would die.

“There is evidence that the queen secretes a chemical that makes the other workers recognize that she is the queen,” said Blonder. “But there’s not much evidence for the queen communicating with the workers in ways beyond that.”

Back in the lab, the ants were placed in artificial nests. “The nice thing about this species is that because they like to live in rock crevices, they’re also completely happy to live between glass slides. All we have to do is take two large glass slides, put a cardboard spacer in between them and the ants happily walk into that very nice thin space and live out their lives in this artificial nest,” said Blonder.

Having secured and relocated several ant colonies, the researchers tackled their second challenge: How to tell two ants apart.

“To understand an interaction network, you need to know who all the individuals are,” said Blonder. “You need to be able to tell any two individuals apart. We accomplished it by painting each ant with a unique color code.”

The researchers filmed the ants with high-definition video and recorded roughly 9,000 interactions between 300 to 400 individual ants. “We watched every single video repeatedly to make sure we didn’t miss any interactions and correctly identified every ant,” said Blonder.

Dornhaus and Blonder recorded every interaction that involved one ant touching another. “We didn’t use visual interactions in this study, and that gave us some ability to standardize,” said Blonder. “There could be many more meaningless visual interactions than meaningless touch interactions because touch definitely conveys some chemical data about the other ant.”

While the ants do have limited vision, it’s thought that most of their sensory input comes through direct chemosensory touch.

Ants antennate, or touch each other with their antennae, for a variety of reasons such as to get another ant to move out of the way, to prod a particularly lazy individual into action or to solicit food. “Not all ants go out and forage for food,” said Blonder. “Often the ants that forage will have whatever they found in their guts and food is transferred from one ant’s stomach through mouth-to-mouth contact to the other ant. It’s called trophallaxis.”

Contrary to predictions that ant networks would spread information efficiently in the same way as other self-directed networks, the researchers found that the ants actually are inefficient at spreading information.

The finding challenges the notion of six degrees of separation, the idea that all individuals in a network are related by six other individuals. For example, I know someone who knows someone who knows someone and so on, and by the sixth person or less I am connected to every person in the world.

This would represent a very efficient network, where it only takes six interactions for information to spread to all of the components. Ant interaction networks apparently function quite differently, indicating that other networks also might not be as efficient as previously thought.

“You could come up with a second simple expectation about how ants might behave,” said Blonder. “They could be just walking around completely randomly bumping into each other. We were able to show that the real ants consistently had rates of information flow that were lower than even that expectation. Not only are they not efficient, they’re also slower than random. They’re actually avoiding each other.”

“So this raises a big question: If you have this ant colony that is presumably very good at surviving and persisting, and there are a lot of good reasons to think it’s optimal to get messages from one part to the other, how come they don’t do it?”

One possible explanation is a concept most of us already are familiar with: “If you spend too much time interacting, then you’re not actually getting anything done,” said Blonder.

Another possibility is that individual ants are responsible for only their region and only need to communicate with other ants in that region.

The research also illustrates the importance of knowing when interactions occur. If two individuals interact and later one of them interacts with a third, then information from the first interaction could be passed to the third individual, but the third individual could not relay information back to the first. “That’s the ordering of events perspective that we’re bringing to this study and we’re hoping is going to catch on with other network studies. We think this is a real opportunity,” said Blonder.

“In some contexts it’s clearly better not to spread information as quickly and then the question becomes understanding in what context it’s good to be efficient and in what context it’s not good to be efficient.”

Understanding how interaction networks function could have applications from allowing us to build self-directed networks to perform specific functions, such as unmanned drones to explore other planets, to preventing the spread of disease.

“Many of these ant species have been on the planet for millions of years, so clearly they’re doing something right,” said Blonder. “Perhaps we could learn from that.”

In the first serious study of the physics of fire-ant rafts, researchers have described how the insects form floating, waterproof islands.

In nature, the rafts allow fire ants to survive epic rainstorms in their native Brazil. In the lab, they could help inspire designs for small, swarming robots that might someday be used to explore inaccessible areas or even clean up oil spills.

“The ant raft, up to this point, has been little more than just categorized and documented,” said mechanical engineer Nathan Mlot of the Georgia Institute of Technology, lead author of a paper in the April 25 Proceedings of the National Academy of Sciences. “We were coming at it from an engineering perspective.”

Ant droplet.

Even though ants’ exoskeletons naturally repel water, a lone ant dropped in a bucket will flounder. But whole colonies of fire ants can float downstream for weeks at a time when flushed from their underground nests. Mlot and his graduate advisor, David Hu, wondered what held the dense mass afloat — and whether it could be harnessed for other applications.

“How are the ants actually linking in the raft?” Mlot said. “We could speculate all we wanted, but the only way to know for sure was to get visual data.”

Mlot’s team collected thousands of fire ants (Solenopsis invicta) by roadsides in Atlanta, where the stinging pests are an invasive species. They immediately noticed that clumps of ants take on the consistency of soft playdough. Ant masses flow like honey or ketchup, and can be described using equations usually found in fluid dynamics.

Antpour

“You could pick up a cluster of these ants and mold it in your hand. You could form it into a ball and toss it up in the air, and all the ants would stay together in one ball,” Mlot said. “They’re almost like a material.”

To set up a reproducible experiment, the team molded ants into balls by swirling them in a beaker. The ants’ natural tendency to stick together made them clump into near-perfect spheres.

Then the researchers placed balls of 500 to 8,000 ants into a water-filled filled container. Th ant sphere almost immediately relaxed into a flat, pancake-shaped raft, with ants on bottom forming a stable layer for the rest of the colony to rest on.

Surprisingly, the whole swarming mass remained delicately balanced atop the water’s surface. When the researchers tried to submerge the raft, water underneath deformed like a stretchy fabric, conforming to the raft’s underside contours.

Focusing on the details of this phenomenon, the researchers subjected their ants to a battery of bizarre tests. To measure how much force one ant could apply to another, they glued live ants to the bottom of a glass slide, then harnessed other ants to them with elastic bands. They painted ants with identification marks and charted their path across rafts. To investigate how the mechanics of raft formation in high resolution, they froze an entire ant raft in liquid nitrogen, then looked at it under a scanning electron microscope.

The images revealed that fire ants grip each other with their mandibles, claws and sticky pads at the end of their feet. Together, they form a tight weave similar to waterproof fabrics like Gore-Tex, which enhances the natural water-repelling properties of their bodies.

The team also built a simple mathematical model of raft formation. It might be used to inspire programs guiding cooperative robots.

“Robotics has often looked at insect communities for inspiration,” said roboticist James McLurkin of Rice University, who designs and builds robot swarms.

Roboticist Seth Goldstein of Carnegie Mellon University suggests that groups of small robots forming antlike rafts could be used to explore sewer lines or waterlogged caves. McClurkin even floated the idea, so to speak, of cleaning oil spills in the Gulf of Mexico.

As for Mlot and his ants, he didn’t lose any sleep over their fate. “After you get bit a couple of times, you lose your sympathy for them,” he said, adding that the experiments are simple enough that anyone can try them at home, “if they’re brave enough.”

Flash memory, scanning tunneling microscopes…and a fly’s sense of smell. According to new research, the same strange phenomenon—quantum tunneling—makes all three possible. If confirmed, the discovery could pave the way for a new generation of artificial scents, from perfumes to pheromones—and, perhaps someday, artificial noses.

The conventional theory of smell holds that the nose’s chemical receptors—some 400 different kinds in a human nose—sense the presence of odorant molecules by a lock-and-key process that reads the odorant’s physical shape. That theory has some problems, though. For instance, ethanol (which smells like vodka) and ethanethiol (which smells like rotten eggs) have essentially the same shape, differing from each other by only a single atom. (Ethanol is C2H6O, and ethanethiol is C2H6S.)

Evidence has emerged over the past decade suggesting that at least part of a molecule’s scent comes from chemical receptors in the nose that pump current through the odorant molecule and cause it to vibrate in an identifiable way. Lacking a direct electrical hookup to the odorant, the nose’s receptors would likely transmit electrons via quantum tunneling, a well-studied process that allows electrons to hop through nonconducting regions if they are small enough. Tunneling is what allows charge to be stored in flash memory cells. It also forms the image in scanning tunneling electron microscopes and is a source of wasted power in microchips.

A group of four scientists from MIT and the Alexander Fleming Biomedical Sciences Research Center, in Vari, Greece, says it has proved the tunneling theory in fruit flies (Drosophila), a favorite lab specimen of geneticists. If the quantum ”molecular vibrational” theory of smell is correct, then the flies should be able to smell the difference between molecules that have regular hydrogen in them versus the same molecules that contain its heavier isotope, deuterium. (The nucleus of regular hydrogen is a proton; the nucleus of deuterium is a proton plus a neutron.)

While regular and ”deuterated” molecules have exactly the same shape, when set in motion by the receptors’ tiny tunneling current, the two would vibrate in a very different pattern of molecular wobbles. A tunneling-based sense of smell should be able to detect the different vibrations. Deuterated molecules would, in other words, smell different to the flies.

According to the new research—published in this week’s Proceedings of the National Academy of Sciences—the flies appear to be able to smell the difference. The researchers had set up a tiny maze with a T-junction. To the right, the molecule acetophenone (which has a sweet and flowery scent to human noses) filled the air. To the left, the air contained an isotope of acetophenone in which eight of the molecule’s hydrogens were swapped out for deuterium. Nearly 30 percent more flies went toward the regular acetophenone. Meanwhile, flies that had been genetically engineered to lack a sense of smell showed no preference.

The group repeated the experiment with a different molecule, octanol, and its deuterated cousin, and got the same result. In a third experiment, the researchers in Greece trained their flies to avoid a deuterated octanol. The vibrations between carbon and deuterium in octanol, says study coauthor Luca Turin, a visiting scientist in biomedical engineering at MIT, are very similar to those of carbon and nitrogen in chemicals called nitriles. So if the vibration theory holds, then some deuterated molecules might share similar odors to the nitriles, even though their shapes are worlds apart.

Indeed, when the trained flies were presented with a whiff of a nitrile, they avoided it. Conversely, flies conditioned to avoid nitriles also avoided the deuterated octanol. ”The only thing the deuterium and nitrile have in common is vibration [pattern],” Turin says.

Andrew Horsfield, senior lecturer in the department of materials at Imperial College London, has been working on early applications of the vibrational theory that Turin’s group tested. Horsfield and his colleagues have developed an indium-arsenide nanowire detector that might crudely ”smell” itself by tunneling electrons between special structures within the nanowire and reading off the vibrations produced. Horsfield’s group plans to extend this idea to smaller devices that can smell external molecules. The group has so far only been fine-tuning its nanowire setup, and Horsfield says its first ”sniff” test might be more than a year away.

Horsfield says that the research being done by Turin’s group justifies his group’s continued nanowire studies. ”It’s very clear to me that this is a very important paper,” he says. ”Time will prove that to be true.”

The way a dragonfly remains stable in flight is being mimicked to develop micro wind turbines that can withstand gale-force winds.

Micro wind turbines have to work well in light winds but must avoid spinning too fast when a storm hits, otherwise their generator is overwhelmed. To get round this problem, large turbines use either specially designed blades that stall at high speeds or computerised systems that sense wind speed and adjust the angle of the blade in response. This technology is too expensive for use with micro-scale turbines, though, because they don’t produce enough electricity to offset the cost. That’s where dragonflies come in.

As air flows past a dragonfly’s thin wings, tiny peaks on their surface create a series of swirling vortices. To find out how these vortices affect the dragonfly’s aerodynamics, aerospace engineer Akira Obata of Nippon Bunri University in Oita, Japan, filmed a model dragonfly wing as it moved through a large tank of water laced with aluminium powder. He noticed that the water flowed smoothly around the vortices like a belt running over spinning wheels, with little drag at low speeds.

Obata found that the flow of water around the dragonfly wing is the same at varying low current speeds, but, unlike an aircraft wing, its aerodynamic performance falls drastically as either water speed or the wing’s size increases. As air flow behaves in the same way as water, this would explain the insect’s stability at low speeds, Obata says.

Obata and his colleagues have used this finding to develop a low-cost model of a micro wind turbine whose 25-centimetre-long paper blades incorporate bumps like a dragonfly’s wing. In trials in which the wind speed over the blades rose from 24 to 145 kilometres per hour, the flexible blades bent into a cone instead of spinning faster. The prototype generates less than 10 watts of electricity, which would be enough to recharge cellphones or light LEDs, the researchers say.

“It’s a clever leap,” says David Alexander, a biomechanics specialist at the University of Kansas. “In some ways it’s more appropriate than using an animal wing model for an airplane. A wind turbine blade is just a wing, only it’s designed to go in tight circles.”

But Wei Shyy of the Hong Kong University of Science and Technology believes that while the dragonfly-inspired design may be more stable, it will also experience more energy loss in terms of drag.

The eyes of moths, which allow them to see well at night, are also covered with a water-repellent, antireflective coating that makes their eyes among the least reflective surfaces in nature and helps them hide from predators in the dark. Mimicking the moth eye’s microstructure, a team of researchers in Japan has created a new film, suitable for mass-production, for covering solar cells that can cut down on the amount of reflected light and help capture more power from the sun.

In a paper appearing in Energy Express, a bi-monthly supplement to Optics Express, the open-access journal published by the Optical Society (OSA), the team describes how this film improves the performance of photovoltaic modules in laboratory and field experiments, and they calculate how the anti-reflection film would improve the yearly performance of solar cells deployed over large areas in either Tokyo, Japan or Phoenix, Ariz.

“Surface reflections are an essential loss for any type of photovoltaic module, and ultimately low reflections are desired,” says Noboru Yamada, a scientist at Nagaoka University of Technology Japan, who led the research with colleagues at Mitsubishi Rayon Co. Ltd. and Tokyo Metropolitan University.

The team chose to look at the effect of deploying this antireflective moth-eye film on solar cells in Phoenix and Tokyo because Phoenix is a “sunbelt” city, with high annual amount of direct sunlight, while Tokyo is well outside the sunbelt region with a high fraction of diffuse solar radiation.

They estimate that the films would improve the annual efficiency of solar cells by 6 percent in Phoenix and by 5 percent in Tokyo.

“People may think this improvement is very small, but the efficiency of photovoltaics is just like fuel consumption rates of road vehicles,” says Yamada. “Every little bit helps.”

Yamada and his colleagues found the inspiration for this new technology a few years ago after they began looking for a broad-wavelength and omnidirectional antireflective structure in nature. The eyes of the moth were the best they found.

The difficulty in making the film, says Yamada, was designing a seamless, high-throughput roll-to-roll process for nanoimprinting the film. This was ultimately solved by Hideki Masuda, one of the authors on the Energy Express paper, and his colleagues at Mitsubishi Rayon Co. Ltd.

The team is now working on improving the durability of the film and optimizing it for many different types of solar cells. They also believe the film could be applied as an anti-reflection coating to windows and computer displays.

In the busy world of a honey bee hive, worker bees need their rest in order to best communicate the location of food to their hive mates, research from The University of Texas at Austin shows.

To deprive honey bees of sleep, Dr. Barrett Klein used a magnetic contraption called the "insominator" (on the left). Sleeping bees affixed with a small piece of metal were jostled awake when the insominator passed over them. Klein found that sleeplessness led to poor signaling by foraging bees about the location of food sources. Credit: Dr. Barrett Klein, pupating.org.

“When deprived of sleep, humans typically experience a diminished ability to perform a variety of tasks, including communicating as clearly or as precisely,” said Dr. Barrett Klein, a former ecology, evolution and behavior graduate student at the university. “We found that sleep-deprived honey bees also experienced communication problems. They advertised the direction to a food site less precisely to their fellow bees.”

For humans, imprecise communication can reduce efficiency, cost money, and in some cases, cost lives. For honey bees, Klein says it could affect their success in locating food, which could lead to a less competitive colony.

“While the importance of sleep has been studied in Drosophila flies for several years,” said Dr. Ulrich Mueller, professor of biology and study coauthor, “Barrett’s study is the first to address the function of sleep in a social insect in the context of its society, and the first to show that sleep deprivation impairs precision of communication in an insect.”

This movie spotlights one waggle dance by a forager that had been sleep-deprived the previous night. The average dance angle of this dance is superimposed over the dancer and variance around this angle indicates imprecision of signaling direction information.

The research was published in PNAS Early Edition this week.

There are various ways to poke and prod humans to force them to stay awake prior to measuring the effects of sleep deprivation. But how to make bees in a hive lose sleep?

Klein invented a magnetic machine aptly named the “insominator,” a contraption he passed over quietly resting bees during the night to deprive them of sleep. The bees, outfitted with small metallic backpacks, were jostled into activity by magnets in the insominator, and this was repeated over the course of normal sleep time.

Barrett then recorded the behaviors of the sleepless bees and discovered they weren’t able to communicate as well the direction of nectar-filled flower patches to their sisters through their usual waggle dance.

“The dance was not necessarily wrong, but it was less precise than dances performed by bees that were not sleep-deprived,” says Klein. “We expect that a less precise dance would lead to fewer followers making it to the food source, and we hope to test this in the future.”